The organic constituents of waste-containing liquids are decomposed by microorganisms by an essentially biological method in treatment plants. There is a microbic increase in the biomass which substantially consists of bacteria with extensive assimilation (i.e., transformation of the organic impurities) in so-called activated sludge tanks under the conditions prevailing therein. After conventional processes have been carried out, the residual content of dissolved, organic sewage constituents is still too high in many cases and does not fulfill the tight regulations regarding the purity of water. Consequently, for many years, numerous attempts have been made and improvements in processes have been sought, to further reduce the content of residual organic sewage constituents. For instance, the throughput in activated sludge tanks (which contain from about 500 to 30,000 m.sup.3) was increased, the concentration of biomasses and oxygen was raised and, in some cases, additional activating tanks were connected in series with the optional use of trickling filter technology. Additional gassing (increased oxygen supply) of the activated sludge was also tested. Moreover, various specific oxidation processes were developed, such as an ozone or hydrogen peroxide treatment.
Furthermore, the catalytic oxidation of the sewage constituents using air and with addition of active carbon in conjunction with subsequent precipitation was recommended (c.f., for example, German Pat. No. 22 39 406; German Offenlegungsschrift No. 30 25 353; A. Bauer et al., Chemie-Technik, Volume 6, pages 3-9 (1982); K. Fischer et al., GWF-Wasser/Abwasser, Volume 2, pages 58-64 (1981): R. E. Perrotti et al., Chemical Engineering Progress (CEP), Vol. 69 (11), 63-64 (1973); G. Wysocki et al., ZC-Chemie-Technik, 3 (6), 205-208 (1974), and 3rd Report "Absorptive Abwassereinigung" (October 1975) published by the Water and Sewage Committee VCIev).
The above-mentioned processes proved to be too complicated or too expensive on an industrial scale. In some cases, the decomposition effect was still unsatisfactory. Numerous attempts to use active carbon in the water treatment industry have failed in the past (despite the improved decomposition effect thereof) because the active carbon, even in its bound (granulated) form is crushed and discharged in too high a quantity even in the very slow currents which are required in settling tanks. Attempts to obtain a sufficiently effective large quantity and to thoroughly bind the active carbon while still maintaining the bioactivity in the settling tank have as yet been unsuccessful.
German Offenlegungsschrift No. 30 32 882 (corresponding to European Patent Application No. 46,900) and German Offenlegungsschrift No. 30 32 869 (corresponding to European Patent Application No. 46,901) describe the use of a macroporous material which has a low specific weight (10-200 kg/m.sup.3) as a carrier material for nitrifying bacteria in activated sludge treatment. These macroporous materials include, for example, polyurethane foams. Similarly, foam particles in a process and an apparatus for anaerobic biological sewage treatment are described. With regard to the improved results achieved, see for example, GWF-Wasser/Abwasser, 124 (1983), Volume 5, 233-239. However, foams of this type float in activated sludge tanks and disturb the process in various ways. Lump foams which are, for example, based on polyurethane have also been recommended in various, specific processes as bulk filling (German Pat. No. 28 39 872 and German Auslegungsschrift No. 2 550 818) or as trickling compositions (Austrian Pat. No. 248 354) for biological sewage treatment.
European Patent Application 77 411 describes the use of polyurethane foam lumps as filtration medium, the impurity content of which is washed away from time to time by specific flushing processes to regenerate the foam.
The combination of surface-active solids with microorganisms to increase the activity thereof in bioconversion processes is also known. German Offenlegungsschriften No. 26 33 259 and German Offenlegungsschriften No. 27 03 834, for example, describe the adsorption of cells on aluminum oxide, bentonites and SiO.sub.2 and the subsequent incorporation thereof into polyacrylates. Furthermore, German Offenlegungsschrift No. 26 29 692 describes the intercalation of cells into photo-hardenable polyurethanes containing photohardenable acrylate double bonds.
The incorporation of cells capable of growth into polyurethane hydrogels is also known, [C.F. for example, Tanaka et al., European Journal of Applied Microbiology and Biotechnology, 7, (1979), from page 351]. German Offenlegungsschrift No. 29 29 872 also describes a process for the production of hydrophilic, gel-like or foamed biocatalysts with a high charge of enzyme-active substance by polymeric inclusion of complete cells, of cell fragments or enzymes, by mixing an aqueous suspension of the enzyme-active substance with hydrophilic polyisocyanates to form a highly enzyme-active hydrophilic polyurethane network in block or bead form. Further publications pertaining to the prior art are noted on page 7 of the above-mentioned Offenlegungsschrift.
The production of polyurethanes which contain enzymatically active substances is difficult and suffers from the disadvantage that it destroys, at least partially, bacteria and cells or deactivates enzymatically active material due to the high reactivity of the isocyanate groups. Residual activities of only 7 to 48%, for example, are shown in the examples of German Offenlegungsschrift No. 29 29 872. It is not desirable to incorporate living bacteria into hydrophilic polyurethanes during production and to use them, for example in treating sewage. The incorporated quantity of bacteria of this type is limited. A significant proportion of the bacteria is also deactivated by the isocyanate reaction. Furthermore, the continuous production of active, bacteria-containing polyurethane compositions and their "activating storage" involves production and storage problems in supplying the treatment tanks which usually contain several thousand cubic meters, with the necessary quantity and concentration of bacteria incorporated in polymers. There would be a drastic reduction in the growth capability of the bacteria even if they were directly incorporated into the treatment plant due to the short survival time when immobilized in the reaction medium.
Consequently, a solution was still sought to the problem of developing new, economical and effective processes for improved sewage treatment.
Thus an object of the present invention is to provide water-absorbing, non-floating, highly-filled polyurethane(urea) compositions which can act as carriers for biomasses in the biological treatment of waste-containing liquids. Such carriers should be accessible and easily producible. Such carrier compositions should not float in the treatment plants, but should remain readily separable. The carriers should be non-abrasive even with respect to added fillers, such as active carbon, common sand and lignite dust, and should represent such a good carrier medium for the colonization of bacteria for decomposing organic materials in the liquids to be treated that there is a greatly improved treatment effect. Treated water of high quality should thereby be obtained.